Cessna TURBO CENTURION T210M 1978 Pilot Operating Handbook page 250

HF TRANSCEIVER
(TYPE PT10-A)
PILOT'S OPERATING HANDBOOK
SUPPLEMENT
SECTION 5
PERFORMANCE
There is no change to the airplane performance when this avionic
equipment is installed. However, the installation of an externally mounted
antenna or several related external antennas, will result in a minor
reduction in cruise performance.
4